Measuring devices are known, which are used in a drilling apparatus to effect seismic measurements exploiting the vibrations produced during drilling in the ground, particularly to determine and acquire reference signals from the source of vibrations, denominated pilot signals, typically used to obtain reliable seismic measurements in this type of device.
A common drilling apparatus generally comprises a tower, a series of rods, coaxial to each other, a motor, which makes the rods rotate, and a drilling element, generally called a bit, mounted on the lower end of said series of rods.
To obtain the desired seismic measurements, during drilling, in one of the typical methods the bit is used as a source of signals. The signals are measured by one or more sensors disposed on the surface of the ground, or in other wells (according to the “cross-hole” technique) adjacent to the excavation, or at a certain distance therefrom, and continuously recorded, or at regular intervals of depth, thus obtaining Vertical Seismic Profiles (VSP) which supply information on the surrounding ground.
In order to be used, a signal supplied by the bit must be identified from among the various noises that are produced during the drilling. To this purpose, the pilot signals are advantageously used. The more reliable the pilot signals are (that is, the greater the signal/noise ratio), the better the geophysical results obtained.
Known measuring devices typically, but not only, effect the measurements of the pilot signals on the series of rods. The measurements are typically, but not only, effected with one or more sensors disposed, in a first solution, on non-rotating parts of the upper part of the series of rods, hereafter denominated head. In another solution, the sensors are inserted in the rods themselves, and therefore also rotate during drilling. In this case, the sensors must be fed with a plurality of electric batteries, or turbine generators mounted on the rods, which entails great complexity in construction and, above all, maintenance problems. Moreover, the data detected by the rotary sensors is disadvantageously recorded locally first and then transmitted when the drilling apparatus is stationary, or is transmitted via radio with a consequent increase in the consumption of electric energy and reduction in autonomy of the batteries.
Another solution for feeding the sensors provides to use sliding contacts with consequent problems of contact, wear, friction and the need to have anti-spark properties, in order to prevent phenomena of deflagration in the case of drilling in the presence of combustible fluids.
To overcome these disadvantages, measuring devices which comprise an electromagnetic induction system (hereafter EMI devices) have also been proposed, which allows both to supply energy to the sensors inserted in the rods and also to transmit the data from the rotary part to a fixed part, mounted on the non-rotary part of the head of the series of rods, or in other parts of the plant. This feed and transmission system comprises a rotary part, functioning as a rotor, and a rotationally fixed part, functioning as a stator, which is disposed in a position of cooperation with a part of the rotor itself, in order to achieve the effect of electromagnetic induction without mechanical contact, thus eliminating the problems connected to wear and friction typical of sliding contacts.
Measuring devices that comprise this electromagnetic induction feed and transmission system cannot, however, be used in drilling apparatuses where the head on which the stator is fixed and the rods move relatively in an axial manner. In this case, the inductive coupling which is achieved by keeping the rotary part and the stator part close together cannot be achieved due to the axial motion of the series of rods. For example, this occurs in drilling apparatuses provided with a so-called top-drive equipment, that is, having the motor mounted directly on the head of the series of rods. In fact, with this configuration, the series of rods can not only rotate but can also slide axially with respect to the motor in order to attenuate, by means of a damping system, the axial stresses caused by the drilling.
One purpose of the present invention is to achieve a measuring device for drilling apparatuses which uses an electromagnetic induction feed and transmission system so that, during drilling, the sensors are fed without suffering from the axial motion of the rods with respect to the mechanical system mounted on the head of the series of rods, or on other parts of the plant, and also so that the measurements effected by the sensors located on the rods themselves are transmitted during the drilling operations of the drilling apparatus.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.